The US Navy is pushing ahead with a radical new cannon that one day could transform how wars are fought, even though some Pentagon officials have voiced concerns over its cost and viability.

Key points:

The US Navy's railgun is a cannon which uses electromagnetic energy

It could eventually travel at seven times the speed at sound

It remains under development but could transform modern warfare

Named the railgun, the weapon in question represents a paradigm shift in ballistic technology.

Instead of using gunpowder and explosive charges to shoot a shell from its barrel, it employs vast amounts of electromagnetic energy to zoom a projectile along a set of copper-alloy rails.

Thanks to four small fins on its rear, the hefty round can then be guided toward a moving object — such as an enemy ship, drone or incoming ballistic missile — relying purely on the kinetic energy from its vast momentum to destroy the target.

Ultimately, scientists expect the railgun rounds to travel at speeds up to Mach 7.5, which at 9,100 kilometres per hour is more than seven times the speed of sound, and cover a distance of about 160 kilometres.

"The railgun is revolutionary in terms of how much it can accelerate the bullet," Tom Boucher, the railgun program manager for Office of Naval Research, told AFP at the Pentagon as he displayed six interconnected steel plates that all had been shredded by a single test round.

"Powder guns have been matured to the point where you are going to get the most out of them. Railguns are just beginning."

The futuristic weapon has long been a darling of the Navy's research wing, along with other game-changing technologies such as laser beams that can track a boat in choppy water and blast holes in its hull.

Jaw-dropping speeds

Yet the railgun, which so far has cost more than $US500 million ($670 million), may find itself becoming something of a victim of its own success — even before it is made operational.

That is because of its special shells designed to hurtle through the skies at jaw-dropping speeds.

These rounds, called High Velocity Projectiles, can be guided in flight.

They can also be fired from a conventional five-inch (12.7 centimetre) cannon.

Though the HVPs would travel slower than they would out of a railgun, they still outperform regular shells, making them a tempting proposition for the Navy to deploy across its fleet.

"It turns out that powder guns firing the same hyper-velocity projectiles gets you almost as much as you would get out of the electromag railgun, and it's something we could do much faster," Deputy Defense Secretary Bob Work told US lawmakers last month.

Each HVP eventually will cost about $US50,000 — still considerably more expensive than a conventional shell but an order of magnitude cheaper than guided missiles such as the Tomahawk, that cost more than $US1 million apiece.

It is not just the Navy with its sights on the railgun.

The Army would one day like to put the electric blasters on its tanks, but is currently constrained the gun's power requirements.

Army Chief of Staff General Mark Milley this week said he envisions a time in the not-so-distant future where railguns and lasers are deployed on land.

"We are looking at all those technologies," he said.

"My professional opinion is that I think we are on the cusp of a fundamental change in the character of ground warfare."